Effects of Tip-Nanotube Interactions on Atomic Force Microscopy Imaging of Carbon Nanotubes

TL;DR

This study uses molecular dynamics simulations to analyze how van der Waals interactions affect AFM imaging of carbon nanotubes, revealing deformation effects and providing guidelines for accurate diameter measurement.

Contribution

The paper demonstrates the impact of tip-CNT interactions on AFM measurements and compares simulation results with experimental data to improve interpretation accuracy.

Findings

AFM can estimate small CNT diameters with good accuracy

Larger CNTs show non-circular cross-sections in AFM images

Knowledge of CNT wall number enhances measurement reliability

Abstract

We examine the effect of van der Waals (vdW) interactions between atomic force microscope (AFM) tips and individual carbon nanotubes (CNTs) supported on SiO2. Molecular dynamics (MD) simulations reveal how CNTs deform during AFM measurement, irrespective of the AFM tip material. The apparent height of a single- (double-) walled CNT can be used to estimate its diameter up to ~2 nm (~3 nm), but for larger diameters the CNT cross-section is no longer circular. Our simulations were compared against CNT dimensions obtained from AFM measurements and resonant Raman spectroscopy, with good agreement for the smaller CNT di-ameters. In general, AFM measurements of large-diameter CNTs must be interpreted with care, but the reliability of the approach is improved if knowledge of the number of CNT walls is avail-able, or if additional verification (e.g. by optical techniques) can be obtained.